Robert Anton Wilson's theory1 is that Dutch was involved with the secret societies that control all of mankind (which, if you look at the strange career of the little gangster, is not unreasonable) and, at the hour of his dying, felt free to reveal their secrets. Unfortunately, delirium and an internal censor prevented him from laying it all out in plainspeak.

1 This theory, of course, is for the purposes of the novel. Although not insupportable, I did not intend to imply that this is RAW's only theory, simply one of many he puts forth in Illuminatus!. Thanks to LudditeAndroid and dTaylorSingletary for the sage advice and needed fixes to this w/u.